Agricultural combines are large machines that harvest, thresh, separate and clean an agricultural crop. The resulting clean grain is stored in a grain tank located on the combine. The clean grain can then be transported from the grain tank to a truck, grain cart or other receiving bin by an unloading auger.
Rotary combines have one or two large rotors for threshing and separating the harvested crop material. In most rotary combines the rotor or rotors are arranged along the longitudinal axis of the machine. These rotors are provided with an infeed section for receiving harvested crop material, a threshing section for threshing the harvested crop material received from the infeed section and a separating section for freeing grain trapped in the threshed crop material received from the threshing section.
Rotors have been provided for combines in a variety of configurations to optimize harvesting efficiency for a wide variety of crops and crop conditions. Examples are shown in U.S. Pat. Nos. 5,445,563 and 5,688,170 assigned to the assignee of the present application. These two patents both disclose rotary crop processing units having two or more sections. The relationship between the rotor axis and the housing axis varies from one section to the other. The rotor axis becomes increasingly offset from the housing axis in the crop flow direction from the housing inlet to the housing outlet. This is accomplished by abrupt transitions in the housing structure between sections where the housing shape changes. As the housing shape changes, the housing axis steps upward relative to the rotor axis and the gap between the rotor and the top of the housing increases at each step in the housing.
U.S. Pat. No. 7,070,498 describes a combine rotor having both infeed and threshing sections on a common frusto-conical portion of the rotor drum. The rotor in the infeed section is provided with helical infeed elements located on the fore-region of the frusto-conical portion of the drum. Immediately downstream from the infeed section, the threshing section is provided with a number of threshing elements. A portion of the threshing elements are attached to the aft-region of the frusto-conical portion of the drum, with the remaining portion being attached to the rearward cylindrical portion.
In such rotary combines, due to the shape and sizing of the housing covers, the rotor housing expands in steps as the material moves rearward. The first step is over the threshing area. The other expansion point is over the separator portion of the rotor. For a rotor design such as disclosed in U.S. Pat. No. 7,070,498, the annular gap defined between the top cover and the rotor tapers to a minimum at the midpoint of the threshing section. The annular gap defined between the rotor and the cover step expands again at the start of the separating section. This abrupt expansion causes excess or wasted power consumption, excess wear and straw damage without increasing threshing capacity.
The present inventors have recognized that a need exists for providing a rotor housing for an axial rotary agricultural combine that provides for efficient energy consumption, an increased wear life, and decreased threshing damage to the grain harvested.